As shown in FIG. 10(a), in general, a traditional tubeless-type heavy-duty pneumatic tire (a) comprises a bead core (c) having a substantially hexagonal in cross-section disposed in a bead portion. Under a condition where the tire is mounted on standard rim (b) and is not yet inflated at an internal pressure (for example, a condition where the tire is reduced in the internal pressure to 5% of the regular internal pressure after inflating to the regular internal pressure), the radially inner surface c1 of the bead core (c) is designed to be substantially parallel to the rim sheet surface b1 of the rim (b), that is to say, to have an angle α1 of substantially 0 degrees between the radial inner surface c1 and a rim sheet surface b1. Accordingly, a fitting pressure between the bead core (c) and the rim (b) uniformly increases at below the bead core (c) so that bead durability and rolling resistance property are improved. An example of a related reference is as follows (see Patent Document 1).
Patent Document 1: Japanese unexamined Patent Application Publication No. 2009-137035.